Distance Attenuation Calculator

Sound energy spreads out spherically as it travels away from its source, causing sound pressure levels (SPL) to drop. In free-field environments, this phenomenon follows the inverse-square law. The decibel reduction over distance is calculated using the formula: SPL2 = SPL1 - 20 * log10(R2 / R1), where SPL1 is the initial sound pressure level at distance R1, and SPL2 is the resulting level at the new distance R2. The difference between the two measurements represents the total attenuation.

Imagine you are measuring a loudspeaker's output at a close distance of 5 meters (R1), where the sound pressure level (SPL1) registers at 90 dB. You want to know what the sound pressure level (SPL2) will be if you move backward to a distance of 20 meters (R2). First, find the distance ratio: 20 / 5 = 4. Next, calculate the base-10 logarithm of 4, which is approximately 0.602. Multiply this by 20 to get 12.04 dB of attenuation. Finally, subtract this attenuation from your initial SPL: 90 dB - 12.04 dB = 77.96 dB. Thus, the sound pressure level at 20 meters is approximately 77.96 dB.

When calculating distance attenuation, always ensure your initial distance and final distance use the same unit of measurement (such as meters or feet). Keep in mind that this calculator assumes an ideal free-field environment without obstacles. In real-world spaces, factors like atmospheric absorption, ground reflections, and barriers will introduce additional attenuation or interference patterns that standard geometric formulas do not capture.